Comparative Behavioral Studies of Indigenous Hemipteran Predators and Hymenopteran Parasites of the Green Cloverworm (Lepidoptera: Noctuidae)

The green cloverworm, Plathypena scabra (F.), is an indigenous pest of soybean and other leguminous crops in the eastern United States. We have recently in vestigated the ecology and behavior of nabid predators of the green cloverworm, as well as the tactics used by four common hymenopteran parasites to overcome the defensive behavior of young green cloverworm caterpillars. Of the three dominant Nabis species in Kentucky agroecosystems, Nabis roseipennis Reuter is the most successful colonist of soy bean fields. Our studies have determined the seasonal phenology, within-plant stratification, and predatory habits of these Nabis species, and we have demonstrated the impact of TV. roseipennis on green cloverworm populations in the field. Three braconid primary parasites and an ichneumonid hyperparasite all must capture young green cloverworms in order to oviposit. Early instars of the green cloverworm usually respond to disturbance from other insects by dropping from the foliage and hanging on silk threads. Each of the four parasites uses a different tactic, or set of tactics, to overcome the caterpillar's defensive behavior. These studies illustrate that taxonomically closely related species, such as nabids, or mem bers of the same ecological guild, such as parasites of young green cloverworm larvae, can exhibit striking behavioral differences. Comparative behavioral studies are an important step in determining the respective roles of these species in the natural biological control of the green cloverworm. Certain hemipteran predators, notably species of Nabis and Orius insidiosus Say, are among the most abundant insect predators in soybean and other crops in the north central United States (Irwin and Shepard, 1980). Both Nabis and Orius species are thought to be important natural enemies of the green cloverworm, Plathypena scabra (F.), an indigenous pest of several leguminous crops (e.g., Pedigo et al., 1983). While Orius is represented by a single abundant species in the eastern United States, Nabis is represented by several species. Unfortunately, due to taxonomic difficulties, Nabis species have generally been lumped together in most studies of these predators in agroecosystems. Several years ago, our observations in soybean and alfalfa caused us to suspect that different nabid species had fun damentally different behaviors which could influence their potential impact on pest species. In addition to presumed mortality from predators, green cloverworms are at tacked by more than 50 species of parasitic Hymenoptera and Diptera (Harper et al., 1983). Different stages, such as eggs and larvae, are attacked by different species of parasites. Within the larval stage, small to medium sized larvae are attacked by different species (primarily hymenopterans) than those attacking me dium to large larvae (primarily dipterans). Here we focus on two lines of study which we have pursued regarding these natural enemies. First, we consider the comparative ecology and behavior of Nabis Accepted for publication 21 October 1988. VOLUME 62, NUMBER 2 157 Table 1. Predicted number of generations per year in central Kentucky for three Nabis species based on developmental rate data collected in the laboratory under eight constant temperature regimes. N. americoferus N. roseipennis N. rufusculus Calculated threshold temperature for total develop ment 11.3?C 11.0?C 11.9?C Mean thermal requirements for total development and pre-oviposition (DDC)a 497.4 610.4 597.7 Range of annual DDC accumulation above threshold forJan.-Oct. in 1983-1986 1844-2047 1900-210